Hi...I'm new to this and need some help. I bought my first lot of fish on Friday, 5 Harlequin Rasbora on the advice of one of my local fish shops, for starting a new tank. They were fine all day Friday and Saturday, but on Sunday evening I noticed one was just floating around on its back, trying to swim but not putting any effort in. I removed it from the tank, and put in in a bowl of treated water at the same temperature. I noticed just before I went to bed that another was doing the same. This morning (monday) that fish had dies along with the one i removed. Another fish is behaving in the same way, but the other two are very healthy. I noticed that the fish weren't eating much either.

May I ask when your tank was set up? I suspect you have New Tank Syndrome situation here. First of all, the tank must be cycled before any fish is added although cycling with fish is acceptable but only hardy fish are permitted for use. The problem with this however is that any fish used in cycling the tank will be subjected to permanent damage and will not thrive for long. There's a sticky thread by fish_4_all in Starting and Maintaining FW Aquariums section which dictates everything you need to know about cycling.:) In cycling, ammonia must spike in the first few days followed by nitrites and finally nitrates.

New Tank Syndrome is a phenomenon where a person adds his/her fish quickly in a newly-uncycled tank. At this rate, ammonia will be present which can be quite toxic to the fish.

I'd recommend you buy API Freshwater Master test kit in liquid form. Check your ammonia, nitrites, nitrates and pH. The test kit is accurate and easy to use. Avoid test strips which do not give accurate results. In the end of cycling, you want zero ammonia and nitrites along with detectable nitrates not exceeding 40 ppm. If you have excess nitrates, carry out a large water change by 60-70% to dilute the nitrates.

Right now, what you must do is stop moving the fish to another bowl and do small daily water changes by 10%. They will be further stressed from being moved after suffering intoxification from nitrites and ammonia.

I'm ready for the pressure.
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I would just like to add that sad as it is that 3 of your fish have died/are unwell, the more fish in the tank while cycling, the worse the ammonia spike will be. So with less fish in the tank now, there is a greater chance of your other 2 making it through the cycle.

The aquarium is only 6 days old, but another fish shop said it would be fine to get hardy fish. What hardy fish would you recommend? What would you have medo? Do you think the remaining two will survive if I do a water change?If they do, roughly how long will it take to fully cycle? If they do all die, what then? Do i need to add amonia to aid the cycle, or should it cycle on its own?

The post Blue directed you to is a good one that explains it all for you. If they all die I would recommend doing a fishless cycle with fish food. This is how I cycled my tank and had no problems.

As for how long it will take, this varies greatly! It can be as little as a week and as much as a few months. Generally the bigger the tank the longer it will take but this isn't a rigid rule.

If you are determined to do a fish cycle, then hardy fish such as danios or sometimes livebearers are often used. How big is your tank? This will hugely impact on what fish and how many you should use.

Its a 35 litre tank, with heater! I don't mind doing a fish food cycle, I've read the posting suggested and think that I can manage if the other 2 do die! It's just a tad depressing when you see them dead and know it's your fault!!!

It is sad, yes, but don't feel too bad. We all have to learn and nobody (or at least nobody on this forum who comes looking for help) ever does it intentionally. Sometimes fish stores aren't as helpful as they could be, and just want a sale, thoguh some are excellent. It's always best to ask about, and do a bit research first.

For a 35litre tank (works out at just under 8 gallons), I wouldn't advise anything other than some tetras, danios, microrasboras (ask Blue about these) or maybe some guppies. Alternatively a betta would look beautiful in a 35litre tank.